This invention relates to the construction of a rotor in a trochoidal rotary internal combustion engine of the spark ignition and compression ignition types.
Rotary piston engines to which the present invention relate have a multilobed piston member (hereinafter referred to as a "rotor") rotatably mounted on a crankpin of a crankshaft, with the crankshaft rotatably mounted in a housing. The multi-lobed rotor has the shape of a trochoid or of a curve inside and parallel to a trochoid, while the housing has an inner surface shape corresponding respectively to the outer enclosing curve, or outer envelope, of the trochoid or of the inside parallel curve; these alternatives hereinafter being encompassed by reference to "trochoid" or the "outer enclosing curve, or envelope" thereof. Rotational phasing of the rotor relative to the shaft and the housing is ensured by an external gear which is fixed to the rotor and which meshes with an internal gear fixed to the housing. The trochoid has at least two lobes and theoretically it can have any greater number of lobes. The number of lobes determines the gear ratio required for phasing and also the number of working chambers in the housing; the number of such chambers being equal to the number of lobes plus one. Thus a family of trochoidal piston rotary engines exists. The present invention is particularly relevant to two lobe trochoid rotary piston engines with three working chambers, and the following description largely is directed to engines having a single two lobe, trochoid shaped rotor. However, the invention extends to engines having more than one rotor and to engines having at least one rotor with three or more lobes.
It is desirable for an engine of this type to have a lightweight rotor to avoid excessive load on a rotor bearing by which the rotor is rotatable on the crankpin, caused by high inertia forces particularly at high speed. For high speed engines it is normal to construct the rotor from an aluminium or magnesium alloy, although it also can be constructed of graphite. However the rotor must be mated to the external gear, with the latter being an external case hardened steel gear for stabilisation purposes, which necessitates the use of a steel hub inserted into the rotor. This steel hub also provides support for the rotor bearing.
Due to different temperature expansion coefficients of the steel hub and the material of which the rotor is constructed, the rotor expands away from the hub. However, it is essential that the hub be locked with the rotor in a manner that prevents this separation, both radially and circumferentially, without risk of distorting the hub or rotor bearing. The present invention provides an arrangement for achieving this.